In water treatment appropriate coagulants are used to improve the removal of many different contaminants. The coagulants initiating the aggregation of the contaminants to large enough particles for removal. A wide variety of coagulants exists, including aluminum salts, iron salts, natural or artificial polyelectrolytes, among others. The roles of the inorganic coagulants (e.g. Fe3+, Al3+) are to neutralize the screening of Coulomb repulsion between the contaminant particulates and/or facilitate the formation of insoluble hydroxide precipitates that serve as nucleation centers for aggregate growth. Both of these functions are highly sensitive to the pH of the source water as the charge on the contaminant particulates as well as the solubility of the hydroxides depends on it. Therefore, proper pH control of the source water is a consideration for efficient contaminant removal.
Conventionally, the inorganic coagulants are introduced into source water in the form of salts having low concentrations of the actual coagulant ions suspended therein. For example, FeCl3*6H2O is a typical coagulant used with salt water, and which contains less than 21% iron by weight.
An alternative to conventional chemical coagulants is electrocoagulation (EC), a method for electrically generating coagulants. In EC the coagulant is produced in the source water directly by the electrochemical dissolution of a sacrificial electrode (e.g. Al, Fe) under an applied voltage. Despite being well known and having the advantage of producing coagulant from compact metal electrodes compared to the use of metal salts with low coagulant ion content, EC is not widely used in the water treatment industry. The lack of use of EC is due in part to the dependency of the electrochemical reactions on source water quality and applied voltage. Another issue is the need for a thorough and rapid mixing of the released coagulant ions into the bulk of the source water. Adjusting the coagulant dose for varying source water quality either requires a change of applied voltage (which can impact the electrochemical reactions occurring inside the EC cell) or a change in the flow rate through the cell (which will impact the mixing efficiency). High salinity liquids, such as sea water or some produced waters, are also challenging to treat with EC, because the high conductivity of these liquids causes a high dosing current even at low voltages, requiring a highly turbulent flow regime within the EC cell to achieve sufficient mixing. Therefore typical EC systems are highly adapted to a specific application with well-defined input waters and are hard to adjust to work for other needs.